In photolithography processes, a photoresist coating system (or “coater”) is connected a chemical supply via one or more conduits, such as pipes, and a filtration system. The filtration system generally includes a filter comprising porous media for filtering particles and other contaminates from the chemical solution, such as photoresist, being supplied to the coater. When a new filter is installed in the filtration system, the chemical solution is used to clean, or flush out, the system, including the conduit and the filter itself. Clearly, this is an expensive process, as the chemical solution itself is expensive and more than two liters of solution is required to accomplish this process. As an alternative, a less expensive chemical solution, or solvent, may be used to clean, or “pre-wet”, the filter off-line, after which the pre-wet filter is installed in the system. Once the filter installed, the system is cleaned using the more expensive chemical solution to flush the filter and tube.
The benefits of employing resist filters as described above include a reduction in operating costs resulting from the extension of the life of the stripping solution, an increase in overall yield as a result of the decrease in the resist carry-through and reduction in downtime, and a decrease in effluent plant demand. In a typical scenario, when a new filter needs to be installed in a tool, the filter is installed in and manually pre-wet at an off-line dummy. Upon completion of the pre-wetting process, the filter is uninstalled from the off-line dummy and installed in the required tool.
Unfortunately, the use of resist filters as described above can induce wafer defects. One such defect may result from insufficient filter pre-wetting, causing a bubble inside the filter that may induce a bridge defect. Another cause of such defects is poor filter quality, in which case a contaminating particle may originate from the filter itself. Yet another cause of such defects is the use of filters whose useful lifetimes are close to expiring or have expired. Additionally, there is a risk of filter contamination each time the filter is installed in and uninstalled from the off-line dummy and the actual tool.